One common technique in the manufacturing of populated circuit cards or circuit boards is to mechanically and electrically connect various components such as I/C chip modules to attachment pads on a substrate, such as epoxy-impregnated fiberglass or polyimide, or other rigid material by flip chip bonding. In connecting the modules, a very common way is to provide a module with what is known as a ball grid array (BGA) of solder balls or column grid array, (CGA) of solder material. The balls or columns are arranged in a pre-determined pattern corresponding to the pattern of attachment pads on the substrate known as a footprint. The module is placed on the substrate with the solder balls or columns contacting the attachment pads. Typically solder paste or the like is applied to the attachment pads on the substrate. This will provide the flux required and also cause the solder balls or columns to adhesively adhere to the attachment pads thus maintaining alignment with the solder balls or columns during heating and reflow of the solder. Heat is then applied to reflow the solder to form a mechanical and electrical connection. In production, this technique works quite well in most instances.
However, sometimes reworking of the populated substrate is required in which a module which has been attached needs to be removed and replaced with another module. This entails melting the solder, removing the module, and cleaning the pads and the substrate. Solder paste then is applied to the pads, and another module is attached by contacting the solder balls or columns thereon with the solder paste and reflowing the solder. In such case of reworking, it is difficult to provide the proper amount of solder paste on each of the pads on the substrate to form the proper bond. It is also necessary to align the solder balls or columns on the module. This is a time-consuming operation and frequently needs several iterations.
Therefore, it is a principal object of the present invention to provide an improved technique for applying the proper amount of solder paste between the attachment pads on a substrate and the solder balls or columns on a grid array contact of module for joining the module to the substrate.